Hello everyone! Just reaching out to narrow the "check list" before I begin. I have a 2005 5.4L 4X4 with 93K miles on it. Was driving at about 30 miles p/h up a hill not wheeling (not very steep) when suddenly the O/D light began blinking and the truck began to lose power. The engine still reved, but had no power. I tried turning the blinking off by pushing the O/D button, but nothing. There was no sign of any problems leading up to this, it just happened. I never tow with it and I don't have a lead foot. The transmission oil is about 30K old or less. Thoughts? Thank you all for your input.

 

The obvious first question is, "How is the fluid level?"

 

... and if the fluid level isn't okay, you're probably looking at an internal transmission failure.

 

Fluid level and color both look good. Other possibilities?

 

In that case either the torque converter is failing, or the tranny is. Either way it's tranny shop time.

 

I know this sounds weird but my '05 Expedition with 122k miles just did the same thing and two days later the alternator went out. I replaced it and it hasn't blinked since. I don't know if it was just a weird coincidence or if there was a connection to the low voltage output.

 

Before I panic and fork out a couple thousand on a transmission, can it be a sensor on or for transmission? If so, any ideas which one? When the truck is in park and I rev the engine, it misses when it hits 3000RPM. It has new plugs and coils and was running great for the last 5000 miles since I replaced the coil packs and plugs.

 

A leaking diode in the alternator *can* cause the alternator to put out too much AC ripple. That can confuse the PCM as it tries to interpret the signal from pulse width modulated sensors as the ripple exaggerates the signal.

 

That's due to the built in rev limiter. It's there to keep people from blowing their engines in park and neutral by over-reving them with no load.

 

So I was remembering back to my brother's 99 Durango that had the same thing happen. The truck just suddenly would not go forward (in my case it does go forward but has no power) and he replaced a sensor that was screwed into the transmission and the problem was solved (it was external). Is there a sensor that communicates with the PCM that can cause this transmission symptom or one that has to do with the gear shift (P D N R 1 2) and the transmission properly shifting into gear. Thank you to those that have replied. thoughts?

 

You sound like you're referring the DTR sensor. (Digital Transmission Range sensor)

 

Could a faulty DTR sensor cause the transmission to not fully engage while allowing the engine speed (RPM) to increase?

 

If faulty it can do all sorts of weird things because the computer thinks the shifter is in a different position than it really is.

 

I thought so. Same question about the Transmission Speed Sensor. Would it cause the symptoms I mentioned?

 

No, if the speed sensor wasn't working, you'd never get out of first gear and the speedometer wouldn't work.